A study of the reliability and validity of the use of death certificate data to assess variations in the hazard of cancer is proposed. The study is novel in its design in that it involves an investigation of the effects of the vital statistics mechanisms in producing official statistics on the causes of death, as well as an investigation of the quality of the original death certificates. A three-year investigation of death certificates for selected counties of known high and low total rates of cancer mortality in North Carolina will be made. The complete death certificate information, including socio-demographic and multiple cause of death data, will be made to assess the relevance of the underlying cause of death, the correspondence with data from hospital and physicians' records, and the overall impact on the epidemiological study of cancer. As the mortality statistics derived from death certificates are often an important factor in basic health policy discussion and, in particular, in setting of priorities for research, the results from this study have important implications for cancer control, treatment, and basic research programs of the National Cancer Institute. It is important that mortality data be consistent with basic epidemiological principles and clinical evidence on the natural history of the disease process, particularly with the notion of multiple conditions leading to death. Furthermore, as much research into population cancer hazards and the effects of environment on occupatonal and population cancer risk is based on death certificate data, the study will yield insights into the epidemiologic concepts and methods employed in such studies.